PH probe for DIY controller

[Squiddy]

I'm building a controller for my 90 gallon and one of the many things that I want to be able to monitor is the PH. I think I have a pretty good idea of how I would go about doing this but I just wanted to see if anyone else here has done this.

The plan is to buy a replacement PH probe from J&L, use an op-amp and amplify the voltage from the probe to a 0-5V scale and put this voltage into one of the A/D's on my controller.

If I could get this to work, then I should be able to apply the same knowledge to a salinity or even a calcium probe and monitor that.

I know other people have built or tried building DIY controllers but I just wanted to see if anyone has interfaced these kind of probes to one.